1. Field of the Invention
This invention relates generally to portable toilets of the type including a bowl unit and a waste holding tank adapted to be detachably secured together with the bowl unit supported on the holding tank.
Typically, the bowl unit has a bowl with an outlet which communicates with an inlet at the top of the holding tank. The holding tank is provided with a valve mechanism which normally closes the inlet but which can be opened to allow waste to enter the holding tank from the bowl. The holding tank also has an outlet which is normally closed, for example by a screw cap, and through which waste can be emptied from the holding tank after the tank has been detached from the bowl unit. The holding tank is designed to be readily portable for this purpose.
A practical problem sometimes encountered in emptying the holding tank is that the waste material may not flow smoothly from the holding tank outlet because the flow of waste material tends to fill or largely obstruct the outlet at least periodically during the emptying cycle. As a result, partial vacuums are intermittently created above the liquid in the holding tank and tend to cause surging or other irregularies in the flow from the tank. This can result in objectionable splashing of the liquid being poured from the tank.
2. Description of the Prior Art
European Patent Application No. 83303054.7 of Thetford Corporation published Dec. 7, 1983 under publication No. 0 095 903 A2 discloses a portable toilet having a manually operable vent valve in the top wall of the holding tank for venting the "head space" of the holding tank during emptying. The valve disclosed in the patent application is spring-biassed to a normally closed position and has an actuator button that must be depressed to hold the valve open against the effect of its spring biassing. In order to be effective, the valve must be held open throughout the operation of emptying the holding tank. A full tank can be quite heavy and the action required to hold the valve open while manipulating the tank to empty its contents is awkward to perform.
An object of the present invention is to provide a portable toilet having an improved vent means.